In a storage control apparatus, data is protected using a technology called RAID (Redundant Array of Independent Disks). In methods that utilize parity like RAID5 and RAID6, even if a portion of the storage devices malfunction, the data stored in the malfunctioning storage devices can be restored based on data of other normal storage devices.
When a failure occurs in any of the multiple storage devices that belong to a parity group (a RAID group), a blocking process is executed. The blocking process is a process for halting the use of a storage device, and isolating this storage device from the system.
The data stored in a blocked storage device is restored to a spare storage device using a process called a rebuild process. That is, in the rebuild process, data (including parity) is read from each of the other, normal storage devices belonging to the same parity group as the blocked storage device, and the data inside the blocked storage device is restored by subjecting these data to a logical operation. The restored data is transferred and written to a spare storage device (an unused storage device). The rebuild process is also called a correction copy process.
However, in recent years there has come to be known a technology called thin provisioning in which a virtual volume is provided to a host computer (hereinafter, host), and an actual storage device is only allocated to an area that has been write-accessed by the host. In thin provisioning, an actual storage area inside a pool is only allocated to the area in which data is actually to be written.
In thin provisioning technology, in a case where a failure occurs in a storage device, a technology for executing the rebuild process only for an area allocated to a virtual volume is known (Patent Literature 1).